1. Field of the Invention
The present invention relates to a method of manufacturing a multilayer ceramic substrate, and more particularly, to a method of manufacturing a multilayer ceramic substrate in which a hard-to-sinter constraining layer for a constrained sintering process is effectively removed to improve quality of the substrate.
2. Description of the Related Art
In general, a multilayer ceramic substrate using glass-ceramics ensures implementation of a three-dimensional inter-layer circuit and formation of a cavity. This allows devices with various functions to be embedded in the multi-layer ceramic substrate, with high flexibility in design.
Accordingly, in the market of smaller and higher-performing high-frequency parts, the multilayer ceramic substrate is increasingly utilized. A multi-layer ceramic substrate in an incipient stage has been manufactured by forming a circuit pattern and a via on a ceramic green sheet as a conductive electrode, arranging and laminating the plurality of green sheets to a desired thickness according to design. In this process, the ceramic substrate shrinks in volume by about 35 to 50%. Particularly, the ceramic substrate shrinks about 12 to 30% in horizontal and vertical lengths, respectively in a transverse direction. This transverse shrinkage can be hardly controlled uniformly. The transverse shrinkage involves an error of 0.5% in respective manufacturing stages and an identical manufacturing stage as well.
With the multilayer ceramic substrate more complicated and precise, inner patterns and via structures have less margin in design and thus constrained sintering is required to suppress transverse shrinkage of the multilayer ceramic substrate.
To this end, a constraining layer made of a hard-to-sinter material such as alumina and barium titanate which is not sintered at a sintering temperature of the ceramic substrate material, is bonded to at least one of two surfaces of the multilayer ceramic substrate in order to suppress shrinkage of the multilayer ceramic substrate in an x-y direction. This hard-to-sinter constraining layer is removed by mechanical machining using e.g., a sandpaper or a polishing process or an ultrasonic device utilizing water and alcohol.
However, the hard-to-sinter constraining layer may not be removed cleanly, thereby hampering a follow-up patterning process.
Notably, even after removal of the constraining layer, a constraining reaction layer formed on a bonding surface by chemical reaction with a composition material of the constraining layer is not removed well by a general method. This leads to plating defects, which subsequently degrade adherence strength in a process such as surface-mount technology (SMT).